Systematic reviews: UKHSA Knowledge and Library Services

Evidence synthesis overview

ContactEvidence oursynthesis teamis the process of bringing together information and knowledge from a variety of sources and disciplines to getinform expertdebates assistance.and decisions on specific issues. (as defined by the Royal Society).

RequestThe supportmain types of evidence synthesis include:

• Systematic reviews 
• Rapid reviews
• Mapping reviews
• Scoping reviews 
• Umbrella reviews

Each follows explicit, systematic methods to collate and synthesise findings
of studies that address a clearly formulated question (as outlined in the Cochrane Handbook, JBI Manual).

The main stages of the evidence synthesis process are shown below:

1. Initial scoping exercise

2. Protocol development

3. Literature searching

4. Screening

5. Data extraction

6. Critical appraisal (optional in rapid mapping and scoping reviews)

7. Synthesis of relevant evidence

Systematic or rapid systematic methodologies

Systematic review methodology

Systematic reviews are the gold standard in evidence synthesis. Systematic review methodologies involve:

• screening, data extraction, critical appraisal and synthesis are performed independently by 2 reviewers (‘in duplicate’), with any discrepancies resolved through discussion, or with a third reviewer
• high rigour and reduced bias 
• considerable time and resources (can take 1 to 2 years)

Rapid review methodology

Rapid reviews use modified systematic methods to accelerate the review process, while maintaining transparency and integrity. For example, rapid review methodologies may:

• search fewer databases or limited grey literature 
• include only one study type, setting, population group or outcome 
• perform limited screening in duplicate (for example, 10% to 20%) 
• use shorter timeframes and limit analyses 
• update a previous systematic review

Key characteristics of the different types of reviews

Systematic reviews

Both systematic methodologies and rapid systematic methodologies can be applied to systematic reviews, scoping reviews, mapping reviews or umbrella reviews.

Systematic reviews should have a specific review question and clearly defined eligibility criteria, usually using the PICO (population, intervention or exposure, comparator, outcome) framework. Study data is summarised using narrative text and tables. Systematic reviews sometimes include a meta- analysis, a statistical technique that provides an overall summary measure of effect.

Systematic reviews should follow the Preferred Reporting Items for Systematic reviews and Meta-Analyses 2020 (PRISMA 2020) guidance. The PRISMA 2020 statement includes a 27-item checklist to support transparent and complete reporting. A PRISMA flow diagram should be included to show the progress of citations through the review.

Scoping reviews

Scoping reviews look at the current state of evidence on a broad topic. They give an overview of what research exists. Scoping reviews are similar to mapping reviews. The key difference is that mapping reviews focus on a specific research question, while scoping reviews explore a wider topic. Scoping reviews usually follow the PCC (Population, Concept, Context) framework instead of the PICO framework.

Scoping reviews are not designed to answer questions like ‘what works…?’. Their aim is to explore a topic, concept or issue to help shape future research or policy development. They do this by clarifying key concepts, definitions or methods.

Scoping reviews tend to be exploratory and may involve refining the process of searching, data extraction and analysis as the review progresses. They tend to have in-depth data extraction, and synthesis can include qualitative analysis, narrative synthesis and/or maps and tables.  The critical appraisal of included studies is optional.

The PRISMA Extension for Scoping Reviews (PRISMA-ScR): Checklist and Explanation can be used for transparent and complete reporting of scoping reviews.

Mapping reviews

Mapping reviews are used to map out and categorise the literature and may be used for broad questions covering a range of interventions, outcomes, and/or populations. They are similar in process to a scoping review, but are based on a specific review question, rather than a topic, and tend to follow the PICO framework.

Mapping reviews are not designed to answer questions like ‘what works…?’. Instead, they show where evidence exists and where there are gaps. This is often presented visually as an evidence gap map. The aim is to inform research priorities, funding, and set a strategic agenda.

Unlike scoping reviews, mapping reviews should use a predefined framework of ‘coding categories’ for the evidence gap map. Apart from the coding categories, data extraction tends to be more limited than for a scoping review. Critical appraisal of included studies is optional, although when conducted it can be represented on the map.

Umbrella review

An umbrella review, or ‘review of reviews’, identifies multiple systematic reviews on related research questions and analyses their results across agreed outcomes. Umbrella reviews normally address a broad scope.

Meta-analysis may be performed to provide an overall summary measure of effect.

Umbrella reviews can only capture evidence that has already been examined in an existing systematic review, so any new evidence would not be included. There are some limitations to these reviews, such as the comprehensiveness of available information provided about the included primary studies.

Assistance KLS provide for systematic and rapidother types of reviews

It is essential that a member of KLS is involved in your review team as early as possible in order to discuss the methodology and process of conducting a review. Any type of systematic review needs to have a well-designed and comprehensive search strategy behind it.it If– if you do not retrieve some of the relevant studies available, the review results will be limited and potentially biased.

ThisDesigning sectiona containsgood informationreview abouttakes howtime, weincluding developing and testing search strategies, which can supportbe youran evidenceiterative review.process. Please contact us to discuss, or see our literature search request page.

Protocol

WeUKHSA canstaff provideare assistancealso preparingable yourto protocol.commission a complete rapid review via one of our UKHSA evidence teams. Visit our page on rapid reviews for details.

Protocol

This describes the rationale and planned methods for your review. It should be written before your review begins and followed when you conduct the review. Guidance on writing a protocol is available in PRISMA for systematic review protocols (PRISMA-P).

You should register your systematic review in the PROSPERO registry.registry This– this should be done before data extraction begins. For further guidance, check the following guide from BioMed Central (BMC): Planning a systematic review? Think protocols.

Literature searching

KLS can provide complex literature searches to help in the production of a systematic review. This involves:

• conducting preliminary scoping searches to find similar reviews (to reduce duplication of effort) 
• developing the search strategy 
• translating the strategy for other databases 
• running the searches on a variety of sources 
  de-duplicating citations 
• providing the results in Endnote or another suitable format 
• citation or similar article searching can also be provided, using sources such as Web of Science, Scopus, PubMed and Google Scholar

Screening

We can advise you on the best way to screen your results and show you tools that can help this process.

Software tools

We offer training and guidance on using tools such as EndNote and EPPI-Reviewer.

Write-up

KLS can write up the methods for your review and help with production of the PRISMA flow diagram.

Examples of reviews

TypesExamples of reviewa systematic review: 

KLS

• Hallmaier-Wacker canL assistand withothers. a‘Incidence varietyand aetiology of evidenceinfant Gram-negative bacteraemia and meningitis: systematic review typesand includingmeta-analysis’. Arch Dis Child 2022: volume 107, issue 11, pages 988 to 994  
• Chu D and others. ‘Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis’. The Lancet 2020: volume 72, issue 4, pages 1500 
• Wolfenden L and others. ‘Strategies for enhancing the implementation of school‐based policies or practices targeting diet, physical activity, obesity, tobacco or alcohol use’. Cochrane Database of Systematic Reviews 2022: volume 8, issue, pages CD011677

Examples of reviews

Examples of a rapid reviews.

systematic review: 

You

• Duval canD contactand usothers. using‘Long our enquirydistance formairborne transmission of SARS-CoV-2: rapid systematic review’ for. moreBMJ information2022: volume 377, page e068743 
• Noone C and weothers. can‘Video helpcalls youfor toreducing choosesocial isolation and loneliness in older people: a rapid review’. Cochrane Database Syst Rev 2020: volume 5, issue 5, page CD013632 
• Rios P and others. ‘Preventing the righttransmission typeof COVID-19 and other coronaviruses in older adults aged 60 years and above living in long-term care: a rapid review’. Syst Rev 2020: volume 9, issue 1, page 218

Examples of a scoping review: 

• O’Toole F and others. ‘What evidence is available on smoking-related diseases beyond those acknowledged by Public Health England? A Scoping Review’. Public Health England 2019  
• Borschmann R and others. ‘The health of adolescents in detention: a global scoping review’. The Lancet Public Health 2020: volume 5, issue 2, pages e114 to e126 
• Belita E and others. ‘A scoping review forof yourstrategies needs.
  to support public health recovery in thetransition to a “new normal” in the age of COVID-19’. BMC Public Health, 2022: volume 22, issue 1, page 1244

UKHSA staff

Examples areof alsoa ablemapping review: 

• Winters N and others. ‘Using mobile technologies to commissionsupport the training of community health  workers in low-income and middle-income countries: mapping the evidence’. BMJ Global Health 2019: volume 4, issue 4, page e001421 
• Saran A and others. ‘Evidence and gap map of studies assessing the effectiveness of interventions for people with disabilities in low-and middle-income countries’. Campbell Systematic Reviews 2020: volume 16, issue 1, page e1070

Examples of a completerapid mapping review:

• Duval D and others. ‘Non-pharmaceutical interventions to reduce COVID-19 transmission in the UK: a rapid mapping review throughand oneinteractive evidence gap map’. Journal of our Public Health 2024: volume 47, issue 2, pages 268 to 302 
• Bosworth M and others. ‘Health equity impact of climate change: a rapid mapping review’. UK Health Security Agency 2022, UKHSA evidence teams. VisitEvidence our Review collection page on(GOV.UK) 2024

Examples of an umbrella review:

• Shah N and others.‘National or population level interventions addressing the social determinants of mental health – an umbrella review’. BMC Public Health 2021: volume 21, issue 1, page 2118 
• Shi X and others. ‘Environmental risk factors for non-Hodgkin’s lymphoma: umbrella review and comparison of meta-analyses of summary and individual participant data’. BMJ Medicine 2022: volume 1, issue 1, page e000184 
• Abu-Odah H and others. ‘Identifying barriers and facilitators of translating research evidence into clinical practice: A systematic review of reviews’. Health Soc Care Community 2022: volume 30, issue 6, pages e3265 to e3276

Example of a rapid reviewsumbrella review:  

• Hatzikiriakidis K and others.  ‘A rapid umbrella review of the literature surrounding the provision of patient-centred end-of-life care’ for. details.
  Palliat Med 2023: volume 37, issue 8, pages 1079 to 1099

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